Cochlear implant drug delivery device

ABSTRACT

Devices for the delivery of a bioactive substance to a cochlea and methods of delivery thereof. The devices include means to allow the release of the bioactive substance within a cochlea.

FIELD OF THE INVENTION

The present invention relates to an implantable device and, inparticular, to an implantable device for use in deliveringpharmaceuticals to a cochlea following implantation of an electrodeassembly.

BACKGROUND OF THE INVENTION

Hearing loss, which may be due to many different causes, is generally oftwo types, conductive and sensorineural. Of these types, conductivehearing loss occurs where the normal mechanical pathways for sound toreach the hair cells in the cochlea are impeded, for example, by damageto the ossicles. Conductive hearing loss may often be helped by use ofconventional hearing aid systems, which amplify sound so that acousticinformation does reach the cochlea and the hair cells.

In many people who are profoundly deaf, however, the reason for deafnessis sensorineural hearing loss. This type of hearing loss is due to theabsence of, or destruction of, the hair cells in the cochlea whichtransduce acoustic signals into nerve impulses. These people are thusunable to derive suitable benefit from conventional hearing aid systems,because there is damage to or absence of the mechanism for nerveimpulses to be generated from sound in the normal manner.

It is for this purpose that hearing implant systems have been developed.Such systems bypass the hair cells in the cochlea and directly deliverelectrical stimulation to the auditory nerve fibres, thereby allowingthe brain to perceive a hearing sensation resembling the natural hearingsensation normally delivered to the auditory nerve.

Hearing implant systems have typically consisted of two key components,namely an external component commonly referred to as a processor unit,and an implanted internal component commonly referred to as areceiver/stimulator unit. Traditionally, both of these components havecooperated together to provide the sound sensation to an implantee.

The external component has traditionally consisted of a microphone fordetecting sounds, such as speech and environmental sounds, a speechprocessor that converts the detected sounds and particularly speech intoa coded signal, a power source such as a battery, and an externalantenna transmitter coil.

The coded signal output by the speech processor is transmittedtranscutaneously to the implanted receiver/stimulator unit situatedwithin a recess of the temporal bone of the implantee. Thistranscutaneous transmission occurs through use of an inductive couplingprovided between the external antenna transmitter coil which ispositioned to communicate with an implanted antenna receiver coilprovided with the receiver/stimulator unit. This communication servestwo essential purposes, firstly to transcutaneously transmit the codedsound signal and secondly to provide power to the implantedreceiver/stimulator unit. Conventionally, this link has been in the formof a radio frequency (RF) link, but other such links have been proposedand implemented with varying degrees of success.

The implanted receiver/stimulator unit typically includes the antennareceiver coil that receives the coded signal and power from the externalprocessor component, and a stimulator that processes the coded signaland outputs a stimulation signal through a lead to an intracochleaelectrode assembly which applies the electrical stimulation directly tothe auditory nerve producing a hearing sensation corresponding to theoriginal detected sound.

The electrode assembly is typically implanted through a cochleostomyformed in the cochlea and comprises an array of electrodes, with eachelectrode being arranged and constructed to deliver a cochleastimulating signal within a preselected frequency range to anappropriate cochlea region. The electrical currents and electric fieldsfrom each electrode stimulate the cilia disposed on the modiolus of thecochlea. Several electrodes may be active simultaneously.

There have been a number of proposals for delivering bioactivesubstances to the cochlea that are beneficial in promoting acceptance ofthe electrode assembly within the cochlea and/or assisting in thefunction of the auditory nerve. One such proposal is described in thepresent applicant's International Application No PCT/AU01/01479 whichdescribes use of a lumen within the electrode assembly that deliversbioactive substances directly within the cochlea following implantationof the assembly.

The present invention provides an alternative system for deliveringbeneficial bioactive substances to the region of the cochlea of apatient and particularly an implantee of a hearing implant.

Any discussion of documents, acts, materials, devices, articles or thelike which has been included in the present specification is solely forthe purpose of providing a context for the present invention. It is notto be taken as an admission that any or all of these matters form partof the prior art base or were common general knowledge in the fieldrelevant to the present invention as it existed before the priority dateof each claim of this application.

SUMMARY OF THE INVENTION

Throughout this specification the word “comprise”, or variations such as“comprises” or “comprising”, will be understood to imply the inclusionof a stated element, integer or step, or group of elements, integers orsteps, but not the exclusion of any other element, integer or step, orgroup of elements, integers or steps.

Generally, the present invention provides a device that is adapted toassist in the delivery of pharmaceutical treatment to surrounding tissuefollowing the insertion and positioning of an electrode assembly.Typically, the electrode assembly is positioned in order to applyelectrical stimulation to a target region of tissue via dedicatedelectrical stimulating electrodes. The present invention is applicableto all types of tissue stimulating devices such as hearing implants,deep brain implants, spinal cord implants and any other implantabledevices that treat neurosensory or motorsensory loss or dysfunction.

It is a preferred feature of the present invention to provide a devicethat is adapted to assist the cochlea in its recovery from traumafollowing the insertion of an electrode assembly therein. The presentinvention is equally applicable to conventional straight electrodeassemblies and electrode assemblies which are designed to conform withthe inner wall of the cochlea.

According to a first aspect, the present invention is a drug deliverydevice comprising:

a resiliently flexible elongate member having a proximal end and adistal end for implantation within a body;

wherein at least a portion of said elongate member is comprised of aporous biocompatible material, at least some of the pores having atleast one bioactive substance disposed therein prior to implantation,said at least one bioactive substance being adapted to migrate from thepores following implantation of the member.

In this aspect, the resiliently flexible elongated member can form partof an implantable tissue-stimulating device having at least oneelectrode mounted thereon.

In another embodiment of this aspect, the drug delivery device can beseparate to a tissue stimulating device but which acts in conjunctionwith said tissue stimulating device.

According to a second aspect, the present invention is an implantabletissue-stimulating device comprising:

a resiliently flexible elongate member having a proximal end and adistal end and at least one electrode mounted thereon between saidproximal and distal ends for delivering electrical stimulation;

wherein at least a portion of said elongate member is comprised of aporous biocompatible material, at least some of the pores having atleast one bioactive substance disposed therein prior to implantation,said at least one bioactive substance being adapted to migrate from thepores following implantation of the member.

In a preferred embodiment of this invention, the device is a Cochlear™implant electrode assembly, with the elongate member adapted to beinserted through a cochleostomy formed in the cochlea and positionedtherein.

In one embodiment, the elongate member can be comprised of one or moreporous portions. In one embodiment, the porous portions can comprise thesame material as the remainder of the elongate member but having aplurality of pores disposed therethrough. In one embodiment, the porousportions can comprise the same material as the remainder of the elongatemember but which has undergone a processing step to render the portionsforaminous. In another embodiment, a majority, or the entire body, ofthe elongate member can be porous.

In one embodiment of this aspect, the elongate member can be formed froma silicone material.

In yet another embodiment, the porous portions can be formed from adifferent material to that of the remainder of the elongate member. Inone embodiment, the porous portions can act as electrodes for deliveringelectrical stimulation at the site of implantation of the elongatemember. In this embodiment, the electrodes can be formed from a suitableporous metallic material. The metallic material can be a suitable porousplatinum. In another embodiment, the porous portions can be formed froma suitable porous metallic material, such as a porous platinum, mountedin the elongate member but where the portions are not adapted to deliverelectrical stimulation.

In one embodiment, all of the electrodes mounted to the elongate membercan be formed from the suitable metallic material, such as a porousplatinum. In another embodiment, only some of the electrodes can beporous, with some of the electrodes being formed from a suitablerelatively non-porous metallic material, such as platinum as isdiscussed in further detail below.

In a still further embodiment, the device can further comprise a sheathcomprised at least in part of a porous material disposed over at least aportion of the elongate member. In a preferred embodiment, a majority ofand, more preferably, the entire elongate member can be sheathed in theporous material. Still further, at least a majority and, morepreferably, the entire sheath is formed of a porous material.

According to a third aspect, the present invention is an implantabletissue-stimulating device comprising:

a resiliently flexible elongate member having a proximal end and adistal end and at least one electrode mounted thereon between saidproximal and distal ends for delivering electrical stimulation; and

a sheath comprised at least in part of a porous material disposed overat least a portion of the elongate member;

wherein at least some of the pores of the sheath have at least onebioactive substance disposed therein prior to implantation, said atleast one bioactive substance being adapted to migrate from the poresfollowing implantation of the member.

According to a fourth aspect, the present invention is an implantabletissue-stimulating device comprising:

a resiliently flexible elongate member having a proximal end and adistal end; and

at least one electrode mounted on the elongate member between saidproximal end and said distal end for delivering electrical stimulation;

wherein at least one of said at least one electrode is comprised of aporous biocompatible material, at least some of the pores having atleast one bioactive substance disposed therein prior to implantation,said at least one bioactive substance being adapted to migrate from thepores following implantation of the member.

In this aspect, said at least one electrode can be formed from asuitable porous electrically conductive material. The electricallyconductive material can be a suitable porous metallic material. Themetallic material can be a suitable porous platinum. In one embodimentof this aspect, all of the electrodes mounted to the elongate member canbe formed from the suitable electrically conductive material, such as aporous platinum. In another embodiment, only some of the electrodes canbe porous, with some of the electrodes being formed from a suitablerelatively non-porous metallic material, such as platinum.

In each of the above aspects, each pore of the porous portion can be anindividual pore within the portion, making no interconnection withanother pore in the portion. In this embodiment, at least some or eachof the pores can be aligned and/or equally spaced with respect to eachother. In another embodiment, some of the pores can be interconnectedwith at least some other pores within the porous portion. In yet anotherembodiment, the pores can be arranged in a random order with some of thepores being interconnected with at least some of the other pores andsome of the pores not interconnected with any of the other pores.

In a further embodiment, at least some of the pores or each pore of theporous portion can be at least substantially uniform in cross-sectionalshape relative to each other. In another embodiment, the pores can varyin cross-sectional shape from one to at least some of the others.

In a still further embodiment, at least some of the pores or each poreof the porous portion can be substantially uniform in diameter. Inanother embodiment, the pores can vary in diameter from one to at leastsome of the others.

In yet another embodiment, at least some of the pores or each pore ofthe porous portion can be of a substantially constant diameter along itslength. In another embodiment, at least some of the pores or each porecan vary in diameter along its length.

In a still further embodiment, at least some of the pores or each poreof the porous portion can have a substantially uniform cross-sectionalshape along its length. In another embodiment, at least some of thepores or each pore can vary in cross-sectional shape along its length.

In yet another embodiment, at least some of the pores or each pore ofthe porous portion can be of a substantially constant length. In anotherembodiment, at least some of the pores or each pore can vary in lengthrelative to at least some of the others in that portion. In oneembodiment, at least some of the pores can have relatively extendedlengths compared to other pores in that portion.

In still another embodiment, at least some of the pores or each pore ofthe porous portion can be at least substantially linear. In anotherembodiment, at least some of the pores or each pore of the porousportion can be non-linear.

In a still further embodiment, at least some of the porous portions oreach porous portion can have substantially the same number of pores perunit area. In another embodiment, at least some of the porous portionsor each porous portion can have differing number of pores per unit arearelative to that of at least some of the other porous portions.

In yet another embodiment, at least some of the pores in one, some oreach of the porous portions can have relatively smooth internal walls.In another embodiment, at least some of the pores in one, some or eachof the porous portions can have rippled internal walls. The ripples canhave a suitably small dimension to preferably at least substantiallyprevent wetting of the cavities thereby minimising friction between thebioactive substance and the walls.

In one embodiment, the nature of the porosity between separate porousportions of the device may be the same or vary from one to at least someor all of the other portions. For example, the dimension of the pores ofa porous portion relatively close to the distal end of the elongatemember may be different to the dimensions of the pores of a porousportion that is relatively close to the proximal end of the elongatemember. In this embodiment, the portion relatively closer to the distalend can have pores having a diameter and/or length greater than thepores of the porous portion relatively closer to the proximal end of theelongate member. In another embodiment, the relative porosity ofdifferent portions can be essentially random.

In a further embodiment, at least some of the pores of the porousportion can be preferably adapted to be at least substantially closedwhen the elongate member is at least substantially straight therebypreventing migration of any bioactive substance held within said atleast some pores from these pores. On adopting a curved configuration,said at least some pores can be adapted to at least partially openallowing migration of the bioactive substance therefrom.

In one embodiment, the bioactive substances can be free to simplymigrate from the pores of the porous portions following implantation ofthe device. In another embodiment, the bioactive substance can bedispersed in a fluid and particularly an ionic fluid that is preferablycaused to migrate from the pores on application of a suitable electricalfield thereto. In another embodiment, the bioactive substance can bedispersed in an ionic solution that is allowed to diffuse from the poresand/or be expelled therefrom under application of a suitable electricfield.

In a fifth aspect, the present invention is a method of delivering atleast one bioactive substance to a desired site of action within acochlea using a device as defined in the above aspects and embodimentsthereof, the method comprising the steps of:

forming a cochleostomy;

inserting the elongate member through the cochleostomy;

allowing or causing the bioactive substance to migrate from the elongatemember into the cochlea.

The pores of the device may be at least partially filled by dipping theelongate member in the bioactive substance for a suitable time period.This step can be performed immediately after manufacture of the elongatemember. In another embodiment, the step can be performed just prior toimplantation of the member into the implantee.

According to a sixth aspect, the present invention is a drug deliverydevice comprising:

a resiliently flexible elongate member having a proximal end and adistal end for implantation within a body;

wherein at least a portion of said elongate member is comprised of abiocompatible polymeric material, having at least one bioactivesubstance impregnated therein, said at least one bioactive substancebeing adapted to diffuse from the polymeric material followingimplantation of the member.

In this aspect, the resiliently flexible elongated member can form partof an implantable tissue-stimulating device having at least oneelectrode mounted thereon.

In another embodiment of this aspect, the drug delivery device can beseparate to a tissue stimulating device but which acts in conjunctionwith said tissue stimulating device

According to a seventh aspect, the present invention is an implantabletissue-stimulating device comprising:

a resiliently flexible elongate member having a proximal end and adistal end and at least one electrode mounted thereon between saidproximal and distal ends for delivering electrical stimulation;

wherein at least one portion of said elongate member is comprised of abiocompatible polymeric material having at least one bioactive substanceimpregnated therein prior to implantation, said at least one bioactivesubstance being adapted to diffuse from the polymeric material followingimplantation of the member.

In a preferred embodiment of this invention, the device is a Cochlear™implant electrode assembly, with the elongate member adapted to beinserted through a cochleostomy formed in the cochlea and positionedtherein.

In another embodiment, said portion of the biocompatible polymericmaterial is fully or partially encapsulated inside the materialcomprising the elongate member. In another embodiment, it can comprise acoating or be relatively near the surface of the elongate member. In oneembodiment, the portion extends into the elongate member from at oradjacent the distal end. In this and other embodiments, the portion canextend for a majority of the length of the elongate member. In anotherembodiment, the portion extends the entire length of the elongate memberbetween the proximal end and the distal end thereof. In this embodiment,said portion can be of constant diameter along its length. In anotherembodiment, said portion can vary in diameter along its length. Forexample, the diameter of said portion can decrease from the proximal endtowards the distal end of the elongate member.

In a still further embodiment, one or more openings can be provided inthe elongate member to allow bioactive substances in said portion todiffuse from said portion and exit the elongate member. An opening canbe provided at the proximal end and/or the distal end of the elongatemember. In another embodiment, there can be one or more openings betweenthe proximal end and the distal end. Where there is more than oneopening, the openings can be regularly or irregularly spaced along theelongate member.

In a still further embodiment, said at least one portion can be disposedin the outer face of the elongate member. In one embodiment, saidportion can comprise a ring member disposed in the outer face of theelongate member. In another embodiment, said portion can comprise aportion of a ring member, such as a half-ring. In another embodiment, anumber of portions can be disposed along the locus of a ring formed inthe outer surface of the elongate member. In a still further embodiment,there can be provided a plurality of rings or ring portions, such ashalf rings, in the outer surface of the elongate member. In theseembodiments, the one or more portions can be at least substantiallyflush with the outer surface of the elongate member. In anotherembodiment, the one or more portions can stand proud of or be recessedin the elongate member.

In a still further embodiment, the portions can be disposed adjacentsaid one or more electrodes in the elongate member. In anotherembodiment, at least one of said portions can be disposed between eachof the electrodes mounted on the elongate member.

In a still further embodiment, one of said portions can be disposedaround one, each of some or each of all the electrodes mounted in theelongate member. Where the electrode comprises a ring or ring portion,the portion can comprise an annular or part-annular member thatsurrounds the electrode.

In yet a further embodiment, the electrode can be disposed around aportion of said biocompatible polymeric material. Where a plurality ofelectrodes are mounted on the elongate member, some or each of theelectrodes can be disposed around separate portions of saidbiocompatible polymeric material.

In one embodiment, the biocompatible polymeric material isnon-degradable and the bioactive substance may be released by gradualdiffusion through the polymeric material. Initially, bioactive substancemolecules closest to the surface of the polymeric material are released.As release continues, molecules must travel a greater distance to reachthe surface and thus the time required for the release increases.Accordingly, the amount of bioactive substance released may decreasewith time.

According to an eighth aspect, the present invention is a drug deliverydevice comprising:

a resiliently flexible elongate member having a proximal end and adistal end for implantation within the body;

wherein at least a portion of said elongate member is comprised of abiodegradable, biocompatible polymeric material having at least onebioactive substance impregnated therein, said at least one bioactivebeing adapted to be released upon at least partial degradation of saidpolymeric material.

According to a ninth aspect, the present invention is an implantabletissue-stimulating device comprising:

a resiliently flexible elongate member having a proximal end and adistal end and at least one electrode mounted thereon between saidproximal and distal ends for delivering electrical stimulation;

wherein at least one portion of said elongate member is comprised of abiodegradable, biocompatible polymeric material having at least onebioactive substance impregnated therein, said at least one bioactivebeing adapted to be released upon at least partial degradation of saidpolymeric material.

The breakdown of the biodegradable polymeric material may occur viagradual hydrolysis of the polymeric material or via biodegradation ofthe polymer structure caused by chemical or enzymatic processes.

Examples of suitable biodegradable polymers include poly(acrylic acid),poly(ethylene glycol), poly(vinylpyrrolidone), poly(hydroxybutyrate),poly(lactide-co-glycolide), polyanhydrides.

According to a tenth aspect, the present invention is a method ofdelivering at least one bioactive substance to a desired site of actionwithin a cochlea using a device as defined in the sixth and seventhaspects, the method comprising the steps of:

forming a cochleostomy;

inserting the elongate member through the cochleostomy;

allowing the bioactive substance to diffuse from the elongate memberinto the cochlea.

According to an eleventh aspect, the present invention is a method ofdelivering at least one bioactive substance to a desired site of actionwithin a cochlea using a device as defined in the eighth and ninthaspects, the method comprising the steps of:

forming a cochleostomy;

inserting the elongate member through the cochleostomy;

allowing or causing at least a portion of the biodegradable,biocompatible polymeric material to at least partially degrade allowingrelease of the bioactive substance therefrom.

According to a twelfth aspect, the present invention is an implantabletissue-stimulating device comprising:

a lead;

a resiliently flexible elongate member extending from the lead andhaving a proximal end and a distal end and at least one electrodemounted thereon between said proximal and distal ends for deliveringelectrical stimulation; and

a bioactive substance delivery means adapted to deliver at least onebioactive substance to the implantee at a location spaced from thedistal end of the member during and/or following implantation of thedevice;

wherein the substance delivery means comprises a body defining a chamberand an outlet in communication with the chamber through which bioactivesubstance can exit the body and further wherein the body is relativelyslidably mounted to the lead of the device.

In a preferred embodiment of this invention, the device is a Cochlear™implant electrode assembly, with the elongate member adapted to beinserted through a cochleostomy formed in the cochlea and positionedtherein. In this embodiment, the outlet of the substance delivery meansis preferably positionable outside and adjacent the cochleostomy site.In this embodiment, the body is preferably relatively slidable along thelead until it reaches a location along the lead that results in it beingpositioned just outside the cochleostomy following implantation.

In a preferred embodiment, the lead can be provided with a stop meansthat prevents the body of the substance delivery means from being movedrelatively past the stop means and onto the elongate member. In anotherembodiment, the stop means can comprise a stop member that, once engagedwith the body, prevents subsequent slidable movement of the collarrelative to the lead in either direction.

In a preferred embodiment, the elongate member is formed from a suitablebiocompatible material.

In a further embodiment, the body of the substance delivery meanscomprises an annular member that is positioned around the lead of thestimulating device. The body preferably has an outer surface. In anotherembodiment, the annular member can comprise a cylindrical collar member.In this embodiment, the body preferably has a longitudinal axis. In oneembodiment, the body can be symmetrical or non-symmetrical about thelongitudinal axis.

In another embodiment, the body can comprise a portion of a ring, suchas a half-pipe.

The annular member can comprise a first portion and a second portion,the second portion having an outer diameter less than that of the firstdiameter. In one embodiment, both the first portion and the secondportion can be cylindrical. In this case, the outer surface preferablyhas a step between the first and second portion. The outer diameter ofthe first portion can be about twice that of the elongate member. In oneembodiment, the first portion can have an outer diameter of about 1.2mm.

In yet a further embodiment, the body can have a proximal end and adistal end. The proximal and distal ends can be at least substantiallyparallel or parallel.

In a further embodiment, the outlet of the body can be positioned in thedistal end of the body. In a still further embodiment, the body can havean inlet in the proximal end of the body. The inlet and outlet arepreferably in communication, such as fluid communication, with eachother.

In a still further embodiment, the outlet of the body can comprise anannular opening in the distal end of the body. The chamber within thebody can extend back into the body from the outlet. Where the outlet isan annular opening, the chamber can also be annular in form and socomprise a cylindrical chamber having an outer and inner surface andextending back into the body from the outlet.

In a still further embodiment, the annular chamber has a region wherethe outer wall of the chamber moves away from the longitudinal axis orthe lead passing through the body as the chamber extends back into thebody from the outlet. In this embodiment, the inner wall of the chambercan also move away from the longitudinal axis or the lead in saidregion. In one embodiment, the chamber can have a frusto-conicalportion. In yet a further embodiment, the chamber can comprise a portiondistal the outlet that is also cylindrical in form. In this embodiment,the inlet preferably comprises a pipe extending from the proximal end ofthe body into the chamber. The inlet is preferably adjacent the outerwall of the body.

In a still further embodiment, the chamber can comprise a pipe extendingfrom the proximal end to the distal end of the body. The pipe ispreferably non-linear. In one embodiment, the inlet can be positioned atleast partially further outwardly from the longitudinal axis of the bodyrelative to the outlet. In this embodiment, the collar can benon-symmetrical about its longitudinal axis.

The distal end of the elongate member is preferably firstly insertedinto the cochleostomy of the implantee during placement of the implant.

The chamber in the body can act as a reservoir for a bioactivesubstance. In one embodiment, the bioactive substance in the reservoircan leach from the chamber into the implantee. In one embodiment, theoutlet can have a semi-permeable membrane. The membrane preferablyallows the bioactive substance to leach from the chamber during and/orfollowing implantation to the desired site of action for the bioactivesubstance.

Where the bioactive substance is carried in or comprises a fluid, thesemi-permeable membrane preferably allows the fluid to leach or diffusetherethrough.

The membrane can act as a valve means that allows fluid to exit thechamber but prevents, or at least substantially prevents, fluid flowfrom external the chamber back into the chamber within the body.

In a further embodiment, the inlet of the body can be in communication,such as fluid communication, with an additional reservoir for thebioactive substance that is external or internal the body of theimplantee. A catheter can extend from the inlet to the additionalreservoir. A pump, such as an osmotic pump, can transfer the bioactivesubstance from the additional reservoir into the chamber of the body forsubsequent delivery to the appropriate site of action.

It is also envisaged that the bioactive substance can be captured in theform of a solid or semi-solid pellet. In one embodiment, the pellet canbe formed by impregnating the bioactive substance in a ceramic or apolymer pellet that has a predetermined rate of release of the bioactivesubstance. This solid pellet can then be stored in the chamber or in anexternal reservoir connectable to the chamber.

The device of this aspect may be adapted to only provide delivery of abioactive substance to the preferred site for a particular periodfollowing implantation. This period may comprise any period of time froma few hours or days to a few weeks or even months. In anotherembodiment, the device can be used as a means of delivery of bioactivesubstances to the implantee well beyond the time of implantation. Forexample, the additional reservoir can be periodically filled with abioactive substance to ensure continued supply of the bioactivesubstance to the implantation site. The additional reservoir, in thiscase, may be positioned beneath but adjacent the surface of the skin ofthe implantee thereby allowing the reservoir to be filled by a syringeand needle assembly that injects the bioactive substance into theadditional reservoir.

According to a thirteenth aspect, the present invention is a method ofdelivering at least one bioactive substance to a desired site of actionadjacent a cochleostomy within a patient using a device as defined inthe twelfth aspect, the method comprising the steps of:

forming a cochleostomy;

inserting the elongate member through the cochleostomy;

closing the cochleostomy; and

slidably positioning the body of the bioactive substance delivery meansadjacent the cochleostomy and allowing said at least one bioactivesubstance to exit therefrom.

The present invention as defined in each of the above aspects provides asurgeon with an implantable component that can be used with a hearingimplant electrode array and that can assist with the delivery of one ormore bioactive substances to a position within the cochlea followingimplantation of the component. The substances that can be delivered bythe present device include substances that are adapted to promotehealing, substances that prevent bleeding or at least excessivebleeding, and also substances that prevent the growth of tissue,including scar tissue, in the cochlea following implantation.Pharmaceutical compounds such as anti-inflammatories and antibiotics canalso be delivered by the present device. It is further envisaged thatthe bioactive substance may comprise a steroid.

In a particularly preferred embodiment, the bioactive substancecomprises a neurotrophic factor including neurotrophins, neuropoietins,insulin-like growth factors, transforming growth factors beta,fibroblast growth factors and other growth factors such as transforminggrowth factor alpha, platelet-derived growth factor and stem cellfactor.

It is also envisaged that substances that assist in reducing the restingpotential of the surrounding neurons can also be delivered by thepresent invention. It should be appreciated that during neuralstimulation the neurons propagate an action potential through theresponse of transmembrane ion channels to local electrical fields. Bydelivering a substance that elicits a change in the transmembranepotential, the resting neural membrane potential can be moved towardsthe activation potential resulting in a lowering of the energy requiredto be delivered to activate the neuron. This also has the potential toreduce the power required by the stimulation device as well as increasethe specificity of the electrical stimulation and restore the stochasticresponse of the neurons.

The device of each aspect may deliver bioactive substances to thepreferred site for a particular period following implantation, from afew hours or days to a few weeks or even months.

In a further embodiment of the above aspects, the elongate member of thestimulating device has a plurality of electrodes mounted thereon. Themember can have a diameter of about 0.6 mm. The member can also have afirst configuration selected to allow said member to be inserted into animplantee's body, such as the cochlea, and a second configurationwherein said elongate member is adapted to apply a preselected tissuestimulation with the electrodes. In a further embodiment, the elongatemember can have at least one intermediate configuration between saidfirst and second configurations.

In a still further embodiment of the above aspects, at least a portionof the outer surface of the elongate member can have a coating oflubricious material. In a further embodiment, a substantial portion ofthe outer surface can have a coating of the lubricious material. In astill further embodiment, the entire outer surface of the elongatemember can have a coating of the lubricious material.

The lubricious material preferably becomes lubricious on being broughtinto contact with a fluid, such as a saline solution. Still further, thecoating preferably becomes lubricious on being brought into contact witha body fluid, such as cochlear fluid.

In one embodiment, the lubricious material is selected from the groupcomprising polyacrylic acid (PAA), polyvinyl alcohol (PVA), polylacticacid (PLA) and polyglycolic acid (PGA). It is envisaged that othersimilar materials could also be used. It is envisaged that thelubricious material can also be impregnated with the bioactive substanceallowing the coating to perform a dual role. The rate of delivery of thebioactive substance can be programmed by design of the coatingstructure.

In yet another embodiment, the device can include a stiffening elementmade of a second material relatively stiffer than the resilientlyflexible material of the elongate member. The stiffening element can beadapted to bias the elongate member into the first configuration.

In a preferred embodiment, the second configuration of the elongatemember is curved. More preferably, the elongate member adopts a spiralconfiguration when in the second configuration.

The elongate member is preferably preformed from a plastics materialwith memory and is preformed to the second configuration. In a preferredembodiment, the first configuration is preferably substantiallystraight. More preferably, the first configuration is straight.

In a preferred embodiment, the elongate member is formed from a suitablebiocompatible material. In one embodiment, the material can be asilicone, such as Silastic MDX 4-4210 or other biocompatible silicones.In another embodiment, the elongate member can be formed from apolyurethane or similar material.

In one embodiment, the stiffening element can comprise a metallicstylet, or a stylet-like element formed from any other suitablestiffening material, extending through a lumen in the elongate member.In one embodiment, the wire can be formed from a biocompatible metal, abiocompatible metallic alloy or a biocompatible relatively stiffplastic. In a preferred embodiment, a metal stylet can be formed fromplatinum.

Once implanted, the electrodes can receive stimulation signals from astimulator device. The stimulator device is preferably electricallyconnected to the elongate member by way of the electrical lead. The leadcan include the one or more wires extending from each electrode of thearray mounted on the elongate member.

In one embodiment, the lead can extend from the elongate member to thestimulator device or at least the housing thereof. In one embodiment,the lead is continuous with no electrical connectors, at least externalthe housing of the stimulator means, required to connect the wiresextending from the electrodes to the stimulator means. One advantage ofthis arrangement is that there is no requirement for the surgeonimplanting the device to make the necessary electrical connectionbetween the wires extending from the electrodes and the stimulatormeans. In this case, the body of the substance delivery means ispreferably positioned around the lead prior to attachment of the lead tothe stimulator device.

The stimulator device is preferably positioned within a housing that isimplantable within the implantee. In the application of the presentinvention to hearing implants, the housing for the stimulator device ispreferably implantable within the bony well in the bone behind the earposterior to the mastoid.

When implantable, the housing preferably contains, in addition to thestimulator device, a receiver device. The receiver device is preferablyadapted to receive signals from a controller means. The controller meansis, in use, preferably mounted external to the body of the implanteesuch that the signals are transmitted transcutaneously through theimplantee.

Signals can preferably travel from the controller means to the receiverdevice and vice versa. The receiver device can include a receiver coiladapted to receive radio frequency (RF) signals from a correspondingtransmitter coil worn externally of the body. The radio frequencysignals can comprise frequency modulated (FM) signals. While describedas a receiver coil, the receiver coil can preferably transmit signals tothe transmitter coil which receives the signals.

The transmitter coil is preferably held in position adjacent theimplanted location of the receiver coil by way of respective attractivemagnets mounted centrally in, or at some other position relative to, thecoils.

In the application of the present invention to hearing implants, theexternal controller can comprise a speech processor adapted to receivesignals output by a microphone. During use, the microphone is preferablyworn on the pinna of the implantee, however, other suitable locationscan be envisaged, such as a lapel of the implantee's clothing. Thespeech processor encodes the sound detected by the microphone into asequence of electrical stimuli following given algorithms, such asalgorithms already developed for Cochlear™ implant systems. The encodedsequence is transferred to the implanted receiver/stimulator deviceusing the transmitter and receiver coils. The implantedreceiver/stimulator device demodulates the FM signals and allocates theelectrical pulses to the appropriate attached electrode by an algorithmwhich is consistent with the chosen speech coding strategy.

For other applications beyond hearing implants, the external controllercan comprise a simple electronic unit capable of being programmed toperform a specific task, such as a predetermined stimulation pattern toa region of the brain or nerves in accordance with a trigger event, suchas a sensed body condition or a patient-triggered action.

The external controller further comprises a power supply. The powersupply can comprise one or more rechargeable batteries. The transmitterand receiver coils are used to provide power via transcutaneousinduction to the implanted receiver/stimulator device and the electrodearray.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example only, a preferred embodiment of the invention is nowdescribed with reference to the accompanying drawings, in which:

FIG. 1 is a pictorial representation of a prior art hearing implantsystem;

FIG. 2 is a simplified view of one embodiment of an elongate memberaccording to one aspect of the present invention;

FIG. 3 is a simplified view of another embodiment of an elongate memberaccording to the present invention;

FIG. 4 is a simplified view of still another embodiment of an elongatemember according to the present invention;

FIGS. 5 a and 5 b are simplified views of yet another embodiment of anelongate member according to the present invention;

FIGS. 6 a and 6 b are simplified views of yet still another embodimentof an elongate member according to the present invention;

FIGS. 7 a, 7 b and 7 c are views of different types of pores accordingto the present invention;

FIG. 8 depicts one type of porous structure for use in one aspect of thepresent invention;

FIG. 9 depicts another type of porous structure for use in the presentinvention;

FIG. 10 a is a simplified enlarged view of one embodiment of a prior artelectrode assembly;

FIG. 10 b is a cross-sectional view of the device of FIG. 10 a;

FIG. 11 is a simplified view of an electrode assembly according toanother aspect of the present invention;

FIGS. 11 a-11 c are cross-sectional views of another embodiment of anelectrode assembly according to this further aspect of the presentinvention;

FIG. 12 is a simplified view of another embodiment of an electrodeassembly according to the further aspect of the present invention;

FIG. 13 is a simplified view of a still further embodiment of anelectrode assembly according to this aspect of the present invention;

FIG. 14 is a simplified view of a still further embodiment of anelectrode assembly according to this aspect of the present invention;

FIG. 15 is a simplified view of a still further embodiment of anelectrode assembly according to this aspect of the present invention;

FIGS. 16 a-16 c are cross-sectional views of an electrode assemblyaccording to this aspect of the present invention;

FIG. 17 is a simplified view of a still further embodiment of anelectrode assembly according to this further aspect of the presentinvention;

FIG. 18 is a simplified view of a further embodiment of an electrodeassembly according to this aspect of the present invention;

FIG. 19 is a simplified cross-sectional view of one embodiment of anelectrode assembly according to another further aspect of the presentinvention;

FIG. 19 a is a cross-sectional view of the device of FIG. 19 throughline AA;

FIG. 19 b is a cross-sectional view of the device of FIG. 19 throughline BB;

FIG. 20 is simplified cross-sectional view of another embodiment of adevice according to this further aspect of the present invention;

FIG. 20 a is a cross-sectional view of the device of FIG. 20 throughline AA; and

FIG. 20 b is a cross-sectional view of the device of FIG. 20 throughline BB.

PREFERRED MODE OF CARRYING OUT THE INVENTION

Before describing the features of the present invention, it isappropriate to briefly describe the construction of one type of knownhearing implant system with reference to FIG. 1.

Known hearing implants typically consist of two main components, anexternal component including a speech processor 29, and an internalcomponent including an implanted receiver and stimulator unit 22. Theexternal component includes a microphone 27. The speech processor 29 is,in this illustration, constructed and arranged so that it can fit behindthe outer ear 11. Alternative versions may be worn on the body. Attachedto the speech processor 29 is a transmitter coil 24 which transmitselectrical signals to the implanted unit 22 via a radio frequency (RF)link.

The implanted component includes a receiver coil 23 for receiving powerand data from the transmitter coil 24. A lead 21 extends from theimplanted receiver and stimulator unit 22 to the cochlea 12 andterminates in an electrode array 20 that is passed through acochleostomy and into the cochlea 12. The signals thus received areapplied by the array 20 to the basilar membrane 8 and the nerve cellswithin the cochlea 12 thereby stimulating the auditory nerve 9. Theoperation of such a device is described, for example, in U.S. Pat. No.4,532,930, the contents of which are incorporated herein by reference.

The array 20 typically comprises an elongate electrode carrier memberhaving a plurality of electrodes mounted thereon. The elongate member isalso typically preformed from a resiliently flexible silicone withmemory and can be preformed to a curved configuration suitable forinsertion in the scala tympani of a human cochlea 12. While an assemblythat normally adopts a curved configuration when in a relaxed conditionis typically preferred, it will be appreciated that the presentinvention also could be utilised with respect to assemblies that arenormally straight when in a relaxed condition.

Still further, the array 20 typically has a lumen that, prior toinsertion of the assembly 20 into the cochlea 12, can receive asubstantially straight platinum stylet. Such a stylet typically has astiffness that is sufficient to retain the silicone elongate member in astraight configuration.

As depicted, the electrode assembly 20 has an electrical lead 21extending back to a receiver/stimulator unit 22. In considering thisinvention, it is to be understood that each electrode may have one ormore wires electrically connected thereto and extending from eachrespective electrode 32 back through the lead 21 to thereceiver/stimulator unit 22.

Various examples of elongate members according to one aspect of thepresent invention are depicted in FIGS. 2 to 6 b. Where electrodes aredepicted in these drawings, it is to be understood that the electrodesare not necessarily shown to scale. A larger number of electrodes thanthat depicted can also be envisaged.

FIG. 2 depicts an elongate member 40 having a plurality of electrodes 41which are formed from a biocompatible porous platinum material. In thedepicted embodiment, each of the electrodes 41 are formed from thismaterial and each adapted to deliver electrical stimulation to thecochlea following implantation. It will be appreciated that in anotherembodiment, only some of the electrodes 41 may be formed from the porousplatinum material, with some of the electrodes being formed from asuitable relatively non-porous metallic material, such as platinum astraditionally used in Cochlear™ implant electrode arrays. In thisembodiment, the electrodes 41 have a bioactive substance disposed withinthe pores of the platinum material that is able to migrate from theelectrodes 41 following implantation of the member 40.

FIG. 3 depicts another embodiment of an elongate member 50 again havinga plurality of electrodes 41 which are formed from a biocompatibleporous platinum material. In this embodiment, however, the elongatemember is provided with a further set of porous platinum rings 51 thatare mounted to the member. As depicted, the rings 51 can be disposedbetween the electrodes 41 mounted on the member. Other locations for therings can be envisaged. In this embodiment, the rings 51, unlike theelectrodes 41, are not adapted to deliver electrical stimulation to theauditory system 12, rather, the electrodes are electrically active butare adapted to create an electrical field to release a drug from themember. If they are electrically active then they can be considered tobe electrically stimulating the cochlea but not necessarily deliveringauditory stimuli thereto. Like the electrodes 41, the depicted rings 51have a bioactive substance disposed within the pores of the platinummaterial that is able to migrate from the rings 51 followingimplantation of the member 50. In a further example, rings 51 may notdeliver electrical stimulation to the auditory system immediately afterimplantation and their role is limited to release of drugs. Once thesupply of drugs has been exhausted, the rings 51 revert to deliveringelectrical stimulation to the auditory system.

The electrical field required for the release of drugs may be created bystimulation in monopolar, bipolar, tripolar, etc mode.

In a further example, the stimulating electrodes are different from thedrug delivering electrodes in either shape and/or in electricalconnection.

While FIG. 3 depicts the rings 51 mounted on a member in conjunctionwith porous platinum electrodes 41, the rings could instead be mountedon an elongate member where some or all of the electrodes are formedfrom a relatively non-porous platinum as is traditionally used inhearing implant electrode arrays.

FIG. 4 depicts a still further embodiment of an elongate member 60 inwhich the material forming the body 61 of the member to which theelectrodes 62 are mounted is formed of porous material, such as a poroussilicone. The pores of the body 61 have a bioactive substance disposedtherein that is able to migrate from the body 61 following implantationof the member 60.

While the depicted electrodes 62 are traditional relatively non-porouselectrodes, it will be appreciated that one, some or all of theelectrodes 62 could be formed from a porous material, such as a porousplatinum.

FIG. 4 also depicts the entire body 61 as being formed from a porousmaterial. In another embodiment, it will be appreciated that only one ormore portions of the body 61 could be formed of such a material.

Where the body 61 is comprised of more than one portion, each of theportions can comprise the same material as the remainder of the elongatemember but having a plurality of pores disposed therethrough. In oneembodiment, the porous portions can comprise the same material as theremainder of the elongate member but which has undergone a processingstep to render the portions foraminous.

In another embodiment, the porous portions of the body 61 can be formedfrom a different material to that of the remainder of the elongatemember.

FIGS. 6 a and 6 b depict a surface of an elongate member 71 that issurrounded by a sheath 72 fabricated from a porous material. Asdepicted, a quantity of bioactive substance 73 can be disposed beneaththe sheath 72 and is free to migrate through the pores 74 in the sheath72 in the direction of arrows A. In this embodiment, it will beappreciated that the elongate member 71 could have one or more of thefeatures of the other elongate members described herein including thosedepicted in FIGS. 2-4.

In each of the embodiments, each pore 81 of the porous material can bean individual pore within the portion, making no interconnection withanother pore in the portion such as is depicted in FIG. 8. In FIG. 8,each of the pores 81 are aligned and equally spaced with respect to eachother.

As depicted in FIG. 9, the porosity can be in essence in threedimensions with some or all of the pores 91 in a porous portion beinginterconnected in some way.

In some or each of the porous portions, at least some of the pores oreach pore of the porous portion can be at least substantially uniform incross-sectional shape relative to each other. In another embodiment, thepores can vary in cross-sectional shape from one to at least some of theothers.

In some or each of the porous portions, at least some of the pores oreach pore of the porous portion can be substantially uniform indiameter. In another embodiment, the pores can vary in diameter from oneto at least some of the others.

In some or each of the porous portions, at least some of the pores oreach pore of the porous portion can be of a substantially constantdiameter along its length. In another embodiment, at least some of thepores or each pore can vary in diameter along its length.

In some or each of the porous portions, at least some of the pores oreach pore of the porous portion can have a substantially uniformcross-sectional shape along its length. In another embodiment, at leastsome of the pores or each pore can vary in cross-sectional shape alongits length.

In some or each of the porous portions, at least some of the pores oreach pore of the porous portion can be of a substantially constantlength. In another embodiment, at least some of the pores or each porecan vary in length relative to at least some of the others in thatportion. In one embodiment, at least some of the pores can haverelatively extended lengths compared to other pores in that portion.

In some or each of the porous portions, at least some of the pores oreach pores of the porous portion can be at least substantially linear,such as respective pores 100 and 101 depicted in FIGS. 7 a and 7 b. Inanother embodiment, at least some of the pores or each pores of theporous portion can be non-linear such as pore 102 depicted in FIG. 7 c.

In some or each of the porous portions, at least some of the porousportions or each porous portion can have substantially the same of poresper unit area. In another embodiment, at least some of the porousportions or each porous portion can have differing number of pores perunit area relative to that of at least some of the other porousportions.

In some or each of the porous portions, at least some of the pores inone, some or each of the porous portions can have relatively smoothinternal walls, such as pore 100 depicted in FIG. 7 a. In anotherembodiment, at least some of the pores in one, some or each of theporous portions can have rippled internal walls, such as pore 101depicted in FIG. 7 b. The ripples can have a suitably small dimension topreferably at least substantially prevent wetting of the cavitiesthereby minimising friction between the bioactive substance and thewalls.

The nature of the porosity between separate porous portions of thedevice may be the same or vary from one to at least some or all of theother portions. For example, the dimension of the pores of a porousportion relatively close to the distal end of the elongate member may bedifferent to the dimensions of the pores of a porous portion that isrelatively close to the proximal end of the elongate member. In thisembodiment, the portion relatively closer to the distal end can havepores having a diameter and/or length greater than the pores of theporous portion relatively closer to the proximal end of the elongatemember. In another embodiment, the relative porosity of differentportions can be essentially random.

In some or each of the porous portions, at least some of the pores ofthe porous portion can be preferably adapted to be at leastsubstantially closed when the elongate member is at least substantiallystraight thereby preventing migration of any bioactive substance heldwithin said at least some pores from these pores. See, for example FIG.5 a which depicts pores 103 as adopting a closed configuration when theelongate member is straight. On adopting a curved configuration, thepores 103 are adapted to at least partially open allowing migration ofthe bioactive substance therefrom, as represented by arrows B.

In this invention, the bioactive substances can be free to simplymigrate from the pores of the porous portions following implantation ofthe device. In another embodiment, the bioactive substance can bedispersed in an ionic fluid that is preferably caused to migrate fromthe pores on application of a suitable electrical field thereto. Inanother embodiment, the bioactive substance can be dispersed in an ionicsolution that is allowed to diffuse from the pores and/or be expelledtherefrom under application of a suitable electric field.

In one embodiment, the bioactive substance can be dispersed in asuitable fluid. In one embodiment, the bioactive substance can comprisea steroid. In another embodiment, the bioactive substance can perform afunction of reducing the resting neuron potential of neurons within thecochlea. The use of such substances can result in less energy beingrequired to excite the neurons and cause stimulation.

In the present invention, the at least one bioactive substance can bedelivered to a desired site of action within a cochlea using a device asdescribed herein. The method preferably comprises the steps of:

forming a cochleostomy;

inserting the elongate member as described herein through thecochleostomy;

allowing or causing the bioactive substance to migrate from the elongatemember into the cochlea.

In this method, the pores of the device are at least partially filled bydipping the elongate member in the bioactive substance for a suitabletime period. This step can be performed immediately after manufacture ofthe elongate member. In another embodiment, the step can be performedjust prior to implantation of the member into the implantee.

FIG. 10 a shows a prior art array 120 comprising an elongate electrodecarrier member 131 having a plurality of electrodes 132 mounted thereon.

As depicted in FIG. 10 b, the array 120 typically has a lumen 134 that,prior to insertion of the assembly 120 into the cochlea, can receive asubstantially straight platinum stylet. Such a stylet typically has astiffness that is sufficient to retain the silicone elongate member 131in a straight configuration.

A resiliently flexible elongate member according to a further aspect ofthe present invention is depicted generally as 140 in FIGS. 11 and 11 a.The member 140 has a plurality of electrodes 132 mounted thereon fordelivering electrical stimulation to the cochlea.

Within the member 140 is at least a partially encapsulated member 141 ofbiocompatible material that has been impregnated with at least onebioactive substance. In this embodiment depicted in FIG. 11, the memberextends for at least a majority of the length of the elongate member andis of a substantially constant diameter along its length.

As can be determined from a comparison of FIGS. 11 a and 11 b, thecross-sectional shape of the member 141 can vary from one array to thenext. Also, in another embodiment as depicted in FIG. 11 c, the member142 can be inserted through the lumen 134 used by the stylet duringimplantation of the array in the cochlea of an implantee.

As depicted in FIGS. 12 and 13, the member 141 can vary in diameteralong its length. For example, as depicted in FIG. 12, the diameter ofthe member 141 can gradually taper from the proximal end towards thedistal end of the elongate member 140. In FIG. 13, the diameterdecreases in a step-wise fashion from the proximal end towards thedistal end.

FIG. 14 depicts a still further embodiment where an impregnatedplug-like member 142 extends into the elongate member 140 from thedistal end thereof.

One or more openings can be provided in the elongate member 140 to allowbioactive substances in the member 141 or 142 to diffuse from the memberand exit the elongate member. Openings can be provided at variouslocations along the member, including the distal end 143 of the elongatemember. Arrows A depict possible locations of diffused bioactivesubstance into the cochlea.

There can instead or also be one or more openings at a location spacedfrom the distal end 143. Where there is more than opening, the openingscan be regularly or irregularly spaced along the elongate member.

As is depicted in FIGS. 15 to 18, the elongate member can haveimpregnated members disposed in the outer face of the elongate member.

As depicted in FIGS. 16 a, 16 b and 16 c, the impregnated members cancomprise a ring member 160 (FIG. 16 a) or a half-ring member 161 (FIG.16 b) disposed in the outer face of the elongate member. In anotherembodiment, the impregnated member can comprise a number of portions 162that are disposed along the locus of a ring formed in the outer surfaceof the elongate member (see FIG. 16 c).

FIG. 15 depicts how a plurality of rings 160 can be disposed between theelectrodes 132 of the array. It will be appreciated that the rings 160of FIG. 15 could be replaced in one, some, or all instances, byhalf-rings 161 or ring portions 162. In the depicted embodiment, thering members 160 stand just proud of the outer surface of the elongatemember. It will be appreciated that one or more of the ring members etccould be at least substantially flush with the outer surface of theelongate member or be recessed in the elongate member.

As depicted in FIG. 17, impregnated portions 170 can be disposed aroundthe electrodes 132 mounted in the elongate member. Where the electrodecomprises a ring or ring portion, the portion can comprise an annular orpart-annular member that surrounds the electrode 132.

As depicted in FIG. 18, the electrode 132 can be disposed around animpregnated portion 180 of biocompatible polymeric material.

One embodiment of a further aspect of a hearing implant electrodeassembly incorporating a system for delivery of bioactive substances isdepicted generally as 230 in FIG. 19.

The assembly 230 includes an elongate member 231 that has a distal end233 that is firstly inserted into the cochlea upon insertion of theassembly 230.

As depicted in FIG. 19, a collar 240 is slidably disposed around thelead 21. The collar 240 is part of a system for delivering one or morepharmaceutical or bioactive substances to a location just external thecochleostomy of the cochlea.

In FIG. 19, the collar 240 can be moved along the lead 21 towards thedistal end 233 of the array member until it reaches a stop member thatprevents further slidable movement of the collar in that direction.

The collar 240 has a stepped outer surface 241 defined by twocylindrical portions 242 and 243. In the depicted embodiment, the collar240 is symmetrical about its longitudinal axis and has parallel proximaland distal ends 244,245.

The outlet 246 of the collar 240 is positioned in the distal end 245 ofthe collar 240. In the depicted embodiment, the collar 240 further hasan inlet 250 in the proximal end 244 of the collar 240. The inlet andoutlet are in communication, such as fluid communication, with eachother.

As depicted in FIG. 19, the outlet 246 of the collar 240 comprises anannular opening in the distal end 245 of the collar. The chamber 247within the collar extends back into the collar 240 from the outlet 246.As the depicted outlet 246 is an annular opening, the chamber 247 isalso annular in form and so comprises a cylindrical chamber having anouter and inner surface and extending back into the collar from theoutlet 246. It will be appreciated, however, that the outlet and chamberneed not be annular to fall within the scope of the present application.

The annular chamber 247 has a frusto-conical region 248 where the outerand inner walls of the chamber 247 move away from the longitudinal axisof the collar 240, and a further cylindrical region 249 distal theoutlet. In this embodiment, the inlet 250 comprises a pipe extendingfrom the proximal end 244 of the collar into the chamber 247. The inlet250 is adjacent the outer wall 241 of the collar 240.

A different construction of a collar is generally depicted as 260 inFIGS. 20, 20 a and 20 b. As depicted, the chamber can instead comprise anon-linear pipe 261 extending from the proximal end 244 to the distalend 245 of the collar 260. The inlet 250 is positioned at leastpartially further outwardly from the longitudinal axis of the collar 260body relative to the outlet 246.

The distal end 233 of the elongate member is preferably firstly insertedinto the cochleostomy of the implantee during placement of the implant.

The chamber in the collar acts as a reservoir for a bioactive substance.This bioactive substance in the chamber diffuses from the chamber intothe implantee through a semi-permeable membrane 270 in the outlet 246.The membrane 270 allows the bioactive substance to leach from thechamber during and/or following implantation to the desired site ofaction for the bioactive substance.

Where the bioactive substance is carried in or comprises a fluid, thesemi-permeable membrane 270 allows the fluid to leach or diffusetherethrough.

The membrane 270 can act as a valve means that allows fluid to exit thechamber but prevents, or at least substantially prevents, fluid flowfrom external the chamber back into the chamber within the body.

A catheter 280 can extend from the inlet 250 to an additional reservoirfor a bioactive substance. A pump, such as an osmotic pump, can transferthe bioactive substance from the additional reservoir into the chamberof the body for subsequent delivery to the appropriate site of action.

It is also envisaged that the bioactive substance can be captured in theform of a solid or semi-solid pellet. In one embodiment, the pellet canbe formed by impregnating the bioactive substance in a ceramic or apolymer pellet that has a predetermined rate of release of the bioactivesubstance. This solid pellet can then be stored in the chamber or in anexternal reservoir connectable to the chamber.

The provision of a system for delivering a pharmaceutical substance inthe cochlea that promotes healing and/or more efficient neuralstimulation while preventing the formation of substantial scar tissue inthe cochlea, enhances the likelihood of successful long-term placementof the elongate member in the cochlea and subsequent successful use ofthe hearing implant by the implantee.

While the preferred embodiment of the invention has been described inconjunction with a hearing implant, it is to be understood that thepresent invention has wider application to other implantable electrodes,such as electrodes used with pacemakers.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive.

1-50. (canceled)
 51. An implantable electrode array assembly configuredto stimulate tissue of a recipient, comprising: an elongate assemblyconfigured to be inserted into a recipient, the elongate assemblyincluding at least one electrode, wherein at least a portion of theelongate assembly contains a bio-active substance.
 52. The implantableelectrode array assembly of claim 51, wherein: one or more portions ofthe elongate assembly are formed of a porous material.
 53. Theimplantable electrode array assembly of claim 51, wherein: the elongateassembly includes one or more members impregnated with the bio-activesubstance.
 54. The implantable electrode array assembly of claim 53,wherein: at least one of the one or more members impregnated with thebio-active substance is located on an outer face of the elongateassembly.
 55. The implantable electrode array assembly of claim 51,wherein: the elongate assembly includes a portion formed from abio-compatible polymeric material, wherein the elongated assembly isconfigured such that the bio-active substance diffuses from thebio-compatible polymeric material following implantation into therecipient.
 56. The implantable electrode array assembly of claim 55,further comprising: an elongate member, wherein the bio-compatiblepolymeric material is at least partially encapsulated within theelongate member.
 57. The implantable electrode array assembly of claim55, wherein: the bio-compatible polymeric material is located at orapproximately at the surface of the elongate assembly.
 58. Theimplantable electrode array assembly of claim 51, wherein: the elongateassembly includes one or more openings which at least partially exposethe bio-active substance to an ambient environment of the elongateassembly.
 59. The implantable electrode array assembly of claim 51,wherein: the bio-active substance is located in a portion of theelectrode array assembly having an outer surface that is substantiallyflush with the outer profile surface of the elongate assembly.
 60. Theimplantable electrode array assembly of claim 51, wherein: thebio-active substance is located in a portion of the electrode arrayassembly having an outer surface that is recessed relative to the outerprofile surface of the elongate assembly.
 61. The implantable electrodearray assembly of claim 51, wherein: the bio-active substance iscontained in one or more portions of the elongate assembly, the one ormore portions of the elongate assembly containing the bio-activesubstance collectively extending for a majority of the length of theelongate assembly.
 62. The implantable electrode array assembly of claim51, wherein: the portion of the elongate assembly that contains thebio-active substance has a diameters that are taken at locations along alongitudinal direction of extension of the elongate assembly that areconstant.
 63. The implantable electrode array assembly of claim 51,wherein: a ratio of a cross-sectional area of the portion of theelongate assembly that contains the bio-active substance when takennormal to a longitudinal direction of the elongate assembly to across-sectional area encompassing an outer profile of the elongateassembly is about constant when the cross-sections are taken atlocations along the longitudinal direction of extension of the elongateassembly.
 64. The implantable electrode array assembly of claim 51,wherein: the elongate assembly includes an elongate member formed from amaterial consisting essentially of silicone; and the portion containingthe bio-active substance is formed from polymeric material.
 65. Theimplantable electrode array assembly of claim 51, wherein: the portioncontaining the bio-active substance is comprised of a biodegradablematerial.
 66. The implantable electrode array assembly of claim 51,wherein: the portion containing the bio-active substance is separatefrom the at least one electrode.
 67. The implantable electrode arrayassembly of claim 51, wherein: the portion containing the bio-activesubstance includes a porous portion having the bio-active substancedisposed therein.
 68. The implantable electrode array assembly of claim67, wherein: elongate assembly is configured such that the bio-activesubstance migrates from the pores to the recipient after implantation ofthe elongate assembly in the recipient.
 69. The implantable electrodearray assembly of claim 51, wherein: elongate assembly is configuredsuch that the bio-active substance migrates, diffuses and/or is releasedfrom the portion containing the bio-active substance after implantationof the elongate assembly into the recipient.
 70. The implantableelectrode array assembly of claim 67, wherein: the porous portion is aporous body that has a substantially uniform porosity.
 71. Theimplantable electrode array assembly of claim 67, wherein: the porousportion has a varying porosity.
 72. The implantable electrode arrayassembly of claim 67, wherein: at least some of the pores of the porousportion are interconnected.
 73. The implantable electrode array assemblyof claim 67, wherein: pores of the porous portion located closer to adistal end of the elongate assembly have a diameter and/or lengthdifferent than those located further from the distal end of the elongateassembly.
 74. The implantable electrode array assembly of claim 67,wherein: pores of the porous portion located closer to a distal end ofthe elongate assembly have a diameter and/or length greater than thoselocated further from the distal end of the elongate assembly.
 75. Theimplantable electrode array assembly of claim 51, wherein the bio-activesubstance is selected from the group consisting of a pharmaceuticalagent, an anti-inflammatory substance, an antibiotic, a steroid, asubstance that reduces a resisting neuron potential of neurons withinthe cochlea, a substance that promotes healing, a substance thatprevents bleeding and/or prevents excessive bleeding, a substance thatprevents the growth of tissue and a substance that promotes moreefficient neural stimulation.
 76. The implantable electrode arrayassembly of claim 51, wherein: the bio-active substance is partiallyencapsulated within the elongate assembly and partially exposed to theexterior of the elongate assembly.
 77. The implantable electrode arrayassembly of claim 51, wherein: the portion of the elongate assembly thatcontains the bio-active substance has diameters that are taken atlocations along a longitudinal direction of extension of the elongateassembly that vary.
 78. The implantable electrode array assembly ofclaim 51, wherein: the portion of the elongate assembly that containsthe bio-active substance has diameters that are taken at locations alonga longitudinal direction of extension of the elongate assembly, thediameters at locations closer to a distal end of the elongate assemblybeing less than diameters at locations farther from the distal end ofthe elongate assembly.
 79. The implantable electrode array assembly ofclaim 51, wherein: elongate assembly is configured such that thebio-active substance migrates, diffuses and/or is released from theportion containing the bio-active substance after implantation of theelongate assembly into the recipient.
 80. The implantable electrodearray assembly of claim 67, wherein: at least some of the pores of theporous portion have a substantially constant size along their length.81. The implantable electrode array assembly of claim 67, wherein: atleast some of the pores of the porous portion have a varying size alongtheir length.
 82. The implantable electrode array assembly of claim 67,wherein: at least some of the pores of the porous portion have asubstantially uniform cross-sectional shape along their length.
 83. Theimplantable electrode array assembly of claim 67, wherein: at least someof the pores of the porous portion have a varying cross-sectional shapealong their length.
 84. The implantable electrode array assembly ofclaim 51, wherein: the portion of the elongate assembly that containsthe bio-active substance is located away from a geometrically centeredlongitudinal axis of the elongate assembly.
 85. The implantableelectrode array assembly of claim 84, wherein: the portion of theelongate assembly that contains the bio-active substance is locatedcloser to a first location on a surface of the elongate assembly than asecond location on the surface of the elongate assembly; the first andsecond locations are located on opposite sides of the elongate assembly;and the at least one electrode is located closer to the second locationthan the first location.
 86. The implantable electrode array assembly ofclaim 84, wherein: the portion of the elongate assembly that containsthe bio-active substance is located on a first side of the geometricallycentered longitudinal axis of the elongate assembly; the at least oneelectrode is located on a second side of the geometrically centeredlongitudinal axis of the elongate assembly; and the first side isopposite the second side relative to the geometrically centeredlongitudinal axis of the elongate assembly.
 87. The implantableelectrode array assembly of claim 51, wherein: the elongate assembly isconfigured to adopt a curved configuration after insertion into acochlea of the recipient to provide stimulation to the cochlea; theportion of the elongate assembly that contains the bio-active substanceis located closer to a first location on a surface of the elongateassembly than a second location on the surface of the elongate assembly;the first location is located on an outermost convex portion of theelongate assembly after the elongate assembly has adopted the curvedconfiguration after insertion into the cochlea to stimulate the cochlea;and the second location is located on an innermost concave portion ofthe elongate assembly after it has adopted the curved configurationafter insertion into the cochlea to stimulate the cochlea.